The present invention relates to organic semiconductors and to the use thereof in organic electronic devices.
Organic semiconductors are being developed for a number of electronic applications of different types. The structure of organic electroluminescent devices (OLEDs) in which these organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. Nos. 4,539,507, 5,151,629, EP 0676461 and WO 98/27136. However, further improvements are still desirable to enable these devices to be used for high-quality and long-lived displays. Thus, in particular, the lifetime and the efficiency of blue-emitting organic electroluminescent devices currently still represent a problem for which there is still a need for improvement. Furthermore, it is necessary for the compounds to have high thermal stability and a high glass-transition temperature and to be sublimable without decomposition. In particular for use at elevated temperature, a high glass-transition temperature is essential in order to achieve long lifetimes.
For fluorescent OLEDs, principally condensed aromatic compounds, in particular anthracene derivatives, are used in accordance with the prior art as host materials, especially for blue-emitting electroluminescent devices, for example 9,10-bis(2-naphthyl)anthracene (U.S. Pat. No. 5,935,721). WO 03/095445 and CN 1362464 disclose 9,10-bis(1-naphthyl)anthracene derivatives for use in OLEDs. Further anthracene derivatives are disclosed in WO 01/076323, in WO 01/021729, in WO 04/013073, in WO 04/018588, in WO 03/087023 or in WO 04/018587. Host materials based on aryl-substituted pyrenes and chrysenes are disclosed in WO 04/016575, host materials based on benzanthracenes are disclosed in WO 08/145,239. For high-quality applications, it is desirable to have available improved host materials. The same also applies to host materials for green- and red-fluorescing dopants.
Prior art which may be mentioned in the case of blue-emitting compounds is the use of arylvinylamines (for example WO 04/013073, WO 04/016575, WO 04/018587). However, these compounds are thermally unstable and cannot be evaporated without decomposition, which requires high technical complexity for OLED production and thus represents a technical disadvantage. It is therefore necessary for high-quality applications to have available improved emitters, particularly with respect to device and sublimation stability and emission colour. It would furthermore be advantageous to have available emitters which have a narrower emission spectrum.
There thus continues to be a demand for improved materials, in particular host materials for fluorescent emitters, especially for green- and red-fluorescing emitters, but also for blue-fluorescing emitters, and fluorescent materials which are thermally stable, which result in good efficiencies and at the same time in long lifetimes in organic electronic devices, which give reproducible results during production and operation of the device and which are readily accessible synthetically. Further improvements are also necessary in the case of hole- and electron-transport materials.
Surprisingly, it has been found that anthracene derivatives which are substituted in the 9- or 9,10-position and onto which an indeno group is condensed in the 1,2-position or 2,3-position or 3,4-position and/or in the 5,6-position or 6,7-position or 7,8-position are very highly suitable for use in organic electroluminescent devices. This likewise applies if corresponding heterocyclic groups, such as, for example, indolo groups or benzothienyl groups, are condensed on instead of the indeno group. These compounds enable an increase in the efficiency and especially the lifetime of the organic electronic device compared with materials in accordance with the prior art. This applies, in particular, to blue-fluorescing devices. Furthermore, these compounds have high thermal stability. In general, these materials are very highly suitable for use in organic electronic devices since they have a high glass-transition temperature. The present invention therefore relates to these materials and to the use thereof in organic electronic devices.
The closest prior art can be regarded as US 2002/132134. This discloses condensed aromatic compounds onto which two aryl-substituted indeno groups are condensed. However, these compounds have a large Stokes shift, which is possibly caused by the degrees of rotational freedom of the aryl substituents. The compounds disclosed in US 2002/132134 are therefore not suitable as host material for deep-blue emitters. There is therefore still a need for improvement here. It would furthermore be advantageous to have available compounds which have a narrower emission spectrum.
Furthermore, 9,10-diphenylanthracene is known as emitter. Although this has a fluorescence quantum efficiency of 100% (H. Du et al., Photochemistry and Photobiology 1998, 68, 141-142), the emission is, however, too far in the blue region, meaning that this compound cannot be used as blue emitter.
For clarity, the structure and numbering of anthracene are shown below:
